Dielectric ceramic matrices with end barriers

ABSTRACT

Multilayer capacitors, and/or circuit structures are formed from monolithic, sintered, ceramic matrices that have a plurality of dielectric or insulating ceramic strata or layers with intervening open-structured areas therebetween, by injecting into said areas molten metal to form internal electrodes or conductors, a penetrable barrier being provided if desired over the entrances to said areas before such injection.

BACKGROUND OF THE INVENTION

This application is in part a continuation of copending application Ser.No. 274,668, filed July 24, 1972 now abandoned, which was in part acontinuation of application Ser. No. 134,689, filed Apr. 16, 1971, nowU.S. Pat. No. 3,679,950.

In the present application and in both the prior applications referredto above, the invention relates to the formation of electrodes and/orconductors in monolithic, sintered, ceramic, dielectric or insulatingbodies and is particularly concerned with the provision of suchelectrodes and/or conductors by a procedure which obviates the necessityof firing them at the same time that the ceramic bodies, with which theyare associated, are fired. Examples of products which may be produced inaccordance with the invention are monolithic, multilayer, capacitors andmultilayer circuit structures such as are used for hybrid integratedcircuits.

Ceramic capacitors have been in use for many years and for many purposeshave replaced paper, mica, and other types of capacitors because of therelatively high dielectric constant of barium titanate and certain otheravailable ceramic materials. This has permitted the production ofhigh-capacitance, miniaturized bodies; and high-speed pressingprocedures have been developed to reduce production costs. However,there has still been a demand for even higher capacities in very smallbodies. Multilayer, monolithic, ceramic capacitors have been produced tomeet this demand.

While there are many variant processes in use for the production of suchmonolithic ceramic capacitors, in a typical process a doctor blade isused to cast on a smooth, non-absorbent surface, a thin layer of asuitable ceramic dielectric composition mixed with a solution of anorganic binder. After the layer dries, the resultant sheet is cut intosmall pieces of rectangular shape to which an electroding paste of anoble metal such as platinum or palladium is applied by a silk-screeningprocedure in such a way that an uncoated margin is left round threesides of the metal coating, but the electroding paste extends to oneedge of the small sheet. A plurality of the small sheets withelectroding paste thereon are then stacked in such a way that onsuccessive sheets the electroding paste coating extends to oppositeedges of the stack. The stack of coated sheets is then consolidated andheated to drive off or decompose the organic binders of the sheets andthe electroding paste and to sinter the dielectric composition into aunitary, monolithic body having electrodes alternately exposed onopposite edge faces. Those electrodes exposed at each edge face are thenconnected together electrically by metallizing the edge faces of thebody where the electrodes are exposed. Thus, there is obtained amonolithic capacitor which may have from a few to a great number, 50 ormore being common, of very thin (often 0.05 mm or less) ceramicdielectric layers. Such capacitors have very high capacitance densitiesand thus the use of extremely small units is permitted in many circuits.

It may be seen from the foregoing description that considerable expenseis involved in such production of monolithic ceramic capacitors becauseof the necessity for using noble metal electrodes. Silver electrodes,such as are commonly used with other ceramic capacitors, are generallyunsuitable for monolithic capacitors where such electrodes, applied asan electroding paste, are fired at the same time as the ceramic layerssince such electrodes are deleteriously affected by such temperatures.

It is, accordingly, one of the objects of the present invention toprovide a process by which the cost of monolithic, ceramic capacitorsmay be reduced by eliminating the use of noble metal electrodes.

Another object of the present invention is to provide a procedure formaking ceramic articles having conductive areas therein which does notrequire the firing of the conductive material at the same time theceramic article is formed by firing.

It is also an object of the present invention to produce multilayercircuit structures for hybrid integrated circuits in which conductorsfor attachment of components are provided at various levels in a ceramicsubstrate or matrix.

SUMMARY OF THE INVENTION

The first two of the above-stated objects are achieved, in accordancewith the teaching of U.S. Pat. No. 3,679,950, by forming a sintered,monolithic, ceramic body which comprises a plurality of thin strata. Thestrata are of two types, strata of one type being dense and imperviousand being formed of ceramic dielectric material with a relatively highdielectric constant, and strata of the other type being of ceramicmaterial having an open, porous structure characterized byinterconnected voids. Strata of one type alternate with strata of theother type through the thickness of the body. This structure can beachieved by introducing between sheets of a powdered, ceramic dielectriccomposition bonded with a temporary bond, a deposit of a temporarilybonded, powdered, ceramic material that on firing develops the desiredopen structure, consolidating a plurality of such sheets withintervening deposits, as described, and firing the consolidated mass tosinter it. Such deposits may be formed in situ, for example by screenprinting or painting, or may be preformed leaves or films, and arearranged so that alternate ones of such open-structured strata extend toa pair of different edge regions of the sintered body. Since thedeposits of the second-mentioned ceramic material, and thus theopen-structured strata, are smaller in area then the dense dielectricstrata, the other edge regions of the fired body and the interiorthereof immediately adjacent the latter-mentioned regions are composedexclusively of the dielectric material. The monolithic ceramic body,after being sintered by firing, is converted to a capacitor byintroducing, e.g. injecting, a molten metal into the open-structuredstrata within the body to form internal electrodes.

The molten metal may be introduced into the open-structured strata andtermination electrodes may then be applied in conventional or desiredmanner on the edge faces of the body having exposed internal electrodes.Alternatively and usually preferably, a penetrable barrier, which may bea termination electrode, can be applied to each edge face having one ormore openings for injection of molten metal, prior to introducing suchmetal into the open-structured strata of said body and the metal canthen be forced through said penetrable barriers into the saidopen-structures strata. If said barriers are not termination electrodes,such electrodes can then be applied after, if necessary or desired,removing all or parts of the barriers. In any event, the presentinvention provides a simple, relatively inexpensive and efficient methodfor forming monolithic capacitors having a very high volume capacitancewhich do not require noble metal internal electrodes and which do notrequire cofiring of metal and ceramic.

A very similar technique can be employed in producing multilayer circuitstructures. For example, thin sheets of a powdered, ceramic, insulatingmaterial temporarily bonded with a fugitive, temporary bond areprovided, by a suitable procedure such as printing, with a desiredpattern of lines, pads, and the like of a ceramic composition (which maybe termed a pseudo-conductor) that on firing develops an open structurehaving interconnected voids as with the above-described bodies. Thesheets are then stacked, compacted, and fired to produce monolithicsintered bodies with predetermined open-structured areas, correspondingto the applied patterns of the pseudo-conductor, which are thenimpregnated with a molten metal to provide conductors in place of thepseudo-conductor.

The term "metal" as used in this specification and the appended claimsis employed broadly to include not only pure and substantially puremetals, but also alloys.

SHORT DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged sectional view of a finished, monolithic, ceramiccapacitor in accordance with the present invention;

FIG. 2 is a sectional view along the plane of the line 2--2 of FIG. 1;

FIG. 3 is a plan view of a bonded sheet of a ceramic dielectriccomposition having deposited thereon, in a pattern, a ceramiccomposition suitable for formation of an open-structured stratum;

FIG. 4 is an enlarged perspective view of two sheets of a bondedceramic, dielectric composition, each sheet having an area thereoncoated with a ceramic composition suitable for formation of anopen-structured stratum;

FIG. 5 is a further enlarged, fragmentary, sectional view of a ceramicbody according to the present invention after assembly and sintering ofa plurality of sheets such as shown in FIG. 4;

FIG. 6 is an enlarged, sectional view of a multilayer ceramic circuitstructure according to the present invention;

FIG. 7 is an enlarged, exploded view showing the several ceramic sheetsforming the structure shown in FIG. 6 with pseudoconductors thereon;

FIG. 8 is a fragmentary, enlarged, sectional view similar to FIG. 5 of aceramic body according to the present invention with a permeable endtermination thereon;

FIG. 9 is an enlarged, fragmentary, sectional view similar to FIG. 5 inwhich instead of a porous strata the planar areas between the dielectricstrata are substantially void;

FIG. 10 is an enlarged, fragmentary, sectional view similar to FIGS. 5and 9 in which the dielectric strata have distinct pillars therebetween;

FIG. 11 is a greatly enlarged view of a bonded, composite, ceramicgranule suitable for use as a pillar;

FIG. 12 is a greatly enlarged, fragmentary, plan view of a bonded leafor sheet of ceramic, dielectric composition having thereon a patternedlayer of thermally-fugitive material adapted for use in a modifiedprocess according to the invention; and

FIG. 13 is a greatly enlarged, fragmentary, sectional view of a sinteredceramic matrix formed from a plurality of leaves such as shown in FIG.12.

DETAILED DESCRIPTION OF THE INVENTION

A process for preparing monolithic ceramic capacitors according to thepresent invention is broadly as follows:

A suitable, finely divided, ceramic, dielectric material is formed intoa thin film with the aid of a suitable, fugitive, heat-removable,film-forming agent. After drying, the film is cut into sheets ofsuitable size. On these sheets is then applied a thin layer, film, orcoating, in a desired pattern, of a suitable paste or the likecontaining a fugitive or heat-removable binder and a powdered ceramiccomposition which when fired at sintering temperatures will, instead ofbecoming dense and compact, form an open structure, i.e. a structure, asubstantial portion of the volume of which is composed of interconnectedvoids. A plurality of the thus-coated ceramic sheets is assembled instacked relation, consolidated into a block, and cut into smaller blocksor chips. The latter are heated to remove the film-forming, temporarybinding agents and are then further heated to a high temperature in airto produce small, coherent, sintered bodies with dense, ceramicdielectric strata alternating with open-structured strata. In each ofthe chips the latter strata extend to an edge face and thus, accordingto the present invention, may be infiltrated or impregnated with aconductive material such as a metal or alloy. Upon suitable infiltrationor impregnation, there is obtained a structure in which there arealternate layers of dielectric material and metal which, when an end ortermination electrode is provided on each end to electrically connectthe metal layers exposed thereon, forms a monolithic capacitor.

The drawings depict such a structure, FIGS. 1 and 2 illustrating on anenlarged and exaggerated scale a monolithic capacitor 11 having thinlayers 13 of dielectric material with thinner layers 15 of conductivematerial such as a metal or alloy, interposed between the layers 13. Aswill be seen in FIG. 1, the layers 15 are so formed that alternate onesextend to the opposite end faces of the capacitor and are thereconnected together electrically by metallizing the ends in a suitable,known, manner to provide the end or termination electrodes 17 and 19.Where, as shown at 21, there is no intervening conductive material, thedielectric layers 13 are united.

In FIG. 3 there is shown a film or sheet 25 of temporarily bondeddielectric material on which a paste or the like, containing a fugitivebinder and a ceramic composition which on firing to sinteringtemperatures will form an open structure, has been printed in smallareas 27 to form a pattern.

In FIG. 4 there are shown, enlarged, two small thin sheets 35 ofdielectric material bonded with a fugitive bond, each of the sheets 35having thereon a layer, film, or coating 37 of a temporarily bonded,ceramic composition that on firing will form a sintered open structure.The sheets 35, which may be formed individually or by appropriatecutting of larger sheets such as the sheet 25 (FIG. 3), are arranged sothat when superimposed or stacked the ends of the layers 37 that entendto the edges of the sheets will be at opposite ends of the stack. When aplurality of such sheets are stacked and fired at sintering temperaturesa structure like that shown in FIG. 5 is obtained.

In FIG. 5 there is shown, further enlarged, a partial sectional view ofa sintered body in accordance with the present invention withalternating dielectric strata 41 and open-structured strata 43, thelatter being adapted to receive a conductive material.

FIGS. 6-13, inclusive, will be hereinafter described in connection withthe description of the structure involved.

The following five examples set forth details of the production ofmonolithic, sintered ceramic matrices suitable for forming ceramiccapacitors according to the present invention.

EXAMPLE 1

An uncalcined ceramic dielectric composition consisting of 93% of bariumtitanate (BaTiO₃) and 7% of bismuth zirconate (Bi₂ O₃ .sup.. 3ZrO₂) isemployed. A mix of 100 g of the dielectric composition in finely dividedform (approximately 1.5 μm particle size) with 65 ml of toluene, 3 gbutyl benzyl phthalate, 10 ml dichlorethane, and 2 ml acetic acid isball milled for 4 hours. To the ball milled product there is then slowlyadded with stirring, an additional 20 ml of dichlorethane and 4 g ofethyl cellulose. If necessary to eliminate bubbles, the stirring may beslowly continued for several hours. A film of the mixture approximately610 mm by 102 mm in area by 0.051 mm thick is formed with a doctor bladeon a sheet of smooth plate glass. When the film dries, the sheet thusformed is removed and small rectangular sheets or leaves approximately102 mm by 51 mm are cut therefrom.

The composition for the open-structured, porous strata is formed from asecond ceramic composition consisting of 66.94% barium carbonate(BaCO₃), 27.1% titanium dioxide (TiO₂), 3.32% bismuth oxide (Bi₂ O₃),and 2.64% zirconium oxide (ZrO₂), all in powdered form, blended in a 1:1weight ratio with a vehicle of the type known as squeegee media which iscomposed of 80 ml pine oil, 14 g acrylic resin, and 1.5 g lecithindispersing agent to which 1.3% (based on the total weight of all otheringredients of the composition) of ethyl cellulose is added to increasethe viscosity. The average particle size of the TiO₂ in the compositionis preferably from about 5 to 10 μm and the particle sizes of the otherceramic ingredients used preferably average from about 1 to 2μm. Thiscomposition is screen printed approximately 0.038 mm thick in arecurring pattern, such as shown in FIG. 3, on the small leaves ofdielectric composition formed as described above. The printed leaves arethen indexed and stacked in groups of 10 so that the printed patterns onalternate leaves are offset. The broken lines 29 in FIG. 3 indicate theplacement of the printed pattern on the sheets above and/or below thesheet 25 when the sheets are stacked. The stacked sheets are pressed atabout 85° C. and 28 kg/cm² to form blocks. The blocks are then cut, bysuitable means such as knives, to form smaller blocks or chips, thecutting being done along such lines as the broken lines 31 and 32, sothat in each of the smaller blocks the alternate strata of screenprinted composition are exposed on opposite ends but are not exposed onthe sides.

The smaller blocks are then heated quite slowly in air to drive offand/or decompose the temporary binding material in the ceramic layersand are thereafter fired at a high temperature, also in air, to formsmall, coherent, sintered chips or bodies.

A suitable heating schedule for removal of the temporary bindingmaterial is as follows:

    ______________________________________                                        100° C. - 16 hours                                                                        295° C. - 2 hours                                   150° C. - 16 hours                                                                        325° C. - 1.5 hours                                 175° C. -  8 hours                                                                        355° C. - 1 hour                                    210° C. - 16 hours                                                                        385° C. - 1 hour                                    225° C. -  8 hours                                                                        420° C. - 0.5 hour                                  250° C. - 16 hours                                                                        815° C. - 0.5 hour                                  ______________________________________                                    

The temperature is then raised to 1260° C. and maintaind for 2 hours tosinter the chips.

The sintered chips obtained, after cooling, may be provided with a metalor alloy in the porous strata and provided with termination electrodeson their opposite ends to obtain efficient monolithic capacitors.

In the foregoing example the porous, open-structured strata of themonolithic ceramic capacitors are essentially the same chemically as thedense dielectric layers, the porosity of the porous strata beingproduced as a result of the decreased volume occupied by the ceramicmaterial used after the reaction thereof which occurs during heating. Inthe following two examples the porous strata are chemically differentfrom the dielectric strata.

EXAMPLE 2

A finely divided (approximately 1.5 μm particle size) ceramic dielectriccomposition consisting of 98% BaTiO₃ and 2% niobium oxide (Nb₂ O₅) isemployed. A mix consisting of 480 g of the powdered dielectriccomposition, 4.8 g of a lecithin dispersing agent, 12.6 g of dibutylphthalate, and 75 ml of toluene is ball milled for 4 hours. There isthen added 156 g of a 40% acrylic resin-- 60% toluene solution. Themixture is slowly stirred for a period of time sufficient to increasethe viscosity by evaporation of solvent and to remove entrapped air. Itis then cast on a smooth glass plate in a sheet about 610 mm square andallowed to dry. The air-dried cast sheets are about 0.07 mm thick andare cut into smaller sheets or leaves approximately 102 mm by 51 mm.

The composition for the porous strata is formed from a second mixtureconsisting of barium oxalate (BaC₂ O₄) and TiO₂ in a 1:1 mol ratio. TheTiO₂, which comprises 26.17% of the mixture, preferably has an averageparticle size of about 2-5μm. The mixture is blended in A 1:1 weightratio with the squeegee medium described in Example 1 and screen printedin a predetermined recurring pattern on the small leaves of dielectricmaterial. The printed leaves are then indexed, stacked 15 high, andcompacted. The thus formed blocks are cut, as in Example 1, to form aplurality of smaller blocks or chips, in each of which alternate layersof the screened-on composition extend to opposite end faces of thechips, but are otherwise inaccessible.

The chips are heated in accordance with a suitable schedule, which maybe the one set forth in Example 1, to eliminate the fugitive binders andare then fired for about 2 hours at about 1325° C. to sinter them. As inExample 1, the strata between the dense dielectric strata have an openstructure comprising a network of interconnected pores and, as a resultof the relatively greater shrinkage when the barium oxalate and TiO₂react to form BaTiO₃, the major portion, by volume, of such strata isvoid. After cooling, the fired chips may be, as hereinafter described,provided with electrodes in the porous areas or strata formed betweenthe dielectric strata and with termination electrodes by suitableprocedure, thereby forming monolithic capacitors.

Even more widely different ceramic materials in the dielectric layersand porous layers respectively, are used in the following example.

EXAMPLE 3

A mixture is made of 472.8 g TiO₂ (average particle size about 1.5 μm),7.2 g kaolin, 4.8 g leciithin dispersing agent, 13.6 g dibutylphthalate, and 75 ml toluene and this mixture is ball milled for 4hours. It is then mixed with 124.9 g of a 1:1 acrylic resin-toluenesolution and, after de-airing, is cast on a smooth glass plate with adoctor blade to a thickness of 0.2 mm to produce on drying a sheet about0.08 mm thick which is cut into smaller sheets approximately 102 mm by51 mm.

Using the procedure of Example 2, the smaller sheets are screen printedin a predetermined recurring pattern with a composition formed by mixing27.58% powdered alumina (Al₂ O₃) having an average particle size of 2.5μm, 14.14% carbon black, and 58.27% of the squeegee medium described inExample 1. The printed sheets are then indexed, stacked 10 high,compacted, and cut to form a plurality of blocks or chips in each ofwhich alternate layers of the screened-on composition extend to oppositeend faces of the chips, but are otherwise inaccessible.

The chips are heated and then fired in substantially the same way as thechips in Example 1, a final firing for 2 hours at about 1320° C. beingemployed. As in Example 1, the open-structured strata between the dense,dielectric, TiO₂ strata have a network of interconnecting pores. Theseresult from the combustion of the carbon black and the larger particlesize of the Al₂ O₃. The porous strata can be impregnated with a metal,by one of the procedures hereinafter disclosed, and provided withsuitably termination electrodes, thereby forming monolithic capacitors.

In the following example another procedure for obtaining bodies withalternate dielectric and open-structured strata is illustrated.

EXAMPLE 4

Small sheets or leaves of a resin-bonded dielectric ceramic compositionare prepared in the manner set forth in Example 2. A screen printingcomposition is made by blending 16 g of the squeegee medium described inExample 1 with 12 g BaTiO₃ (approximatey 4 μm particle size) and 4 gcarbon black, Stoddard solvent being added as necessary to obtain thedesired viscosity. This composition is then screened on the leaves inthe same manner as in Example 2 and allowed to dry. Blocks and smallercut blocks or chips are formed from the printed leaves in the same wayas in Example 2 and the chips are heated and fired, also in the sameway. In the course of the firing the carbon black burns out leaving anopen-structure comprising a network of interconnected pores in the areasbetween the dense dielectric strata. The use of the relatively coarseBaTiO₃ in the printing composition increases the porosity. These porousareas can be filled with a metal in one of the ways described andprovided with end elecrodes to form monolithic capacitors.

Still another way of forming monolithic ceramic capacitors according tothe principles of the present invention is illustrated in the followingexample.

EXAMPLE 5

A sheet about 0.08 mm thick of a ceramic dielectric material such as theone produced in Example 2 is cut into smaller sheets or leavesapproximately 20 mm by 20 mm. Another sheet of slightly less thickness,for providing porous strata, is formed by casting a composition formedfrom 351 g BaTiO.sub. 3, 7 g Nb₂ O₅, and 115 g carbon black, theseingredients being ball milled for several hours with toluene and dibutylphthalate and then, after admixture with a 1:1 acrylic resin-toluenesolution, de-aired before casting. The second sheet is cut into leavesapproximately 13 mm by 16 mm. The leaves of dielectric material and ofthe other ceramic material are then stacked 11 high. Thesecond-mentioned leaves are alternated with the leaves of dielectricmaterial and have their long side edges aligned and equally spaced fromthe edges of the larger leaves. Alternate leaves of the secondcomposition are laid in place so that the ends thereof extend toopposite edges of the dielectric material leaves. The stack is thenconsolidated by pressing at about 7 kg/cm² and a temperature of about40° C. and the consolidated block is heated to burn out the temporarybinders and the carbon black and to sinter the ceramic materials into astructure in which open-structured, porous, ceramic strata alternatewith dense, ceramic, dielectric strata. A heating schedule like thatspecified in Example 1 is used, the final heating, however, being at1370° C. for 2 hours firing being in the air. The fired block may beimpregnated with a metal in the porous strata, thereby forming internalelectrodes, by any of the procedures described hereinafter. Suitabletermination electrodes can also be provided.

Although in Examples 1- 2, the dielectric materials used are modifiedbarium titanate compositions, it will be clear that others of the largenumber of ceramic dielectric compositions known may also be used. Forexample, TiO₂ (note Example 3), glass, steatite, and barius strontiumniobate, as well as barium titanate alone can be used, suitable changeswell known in the art being made as required in firing conditions andthe like to achieve proper sintering. Obviously, the capacitance of theresulting capacitors will vary as a result of using materials withhigher or lower dielectric constants.

It will also be understood that the composition of the open-structuredstrata in ceramic chips according to the invention may vary widely. Notonly may the open-structure be achieved by use of a composition which isidentical with or similar to the composition of the dielectric strata,although having a greater shrinkage on firing, but also the compositionmay be quite different, as for example, in Example 3. An open-structuremay also be produced or the void volume of such structure be increasedby other means, for example by employing a combustible material in themix as illustrated in Examples 3 and 5. It is important, however, toemploy materials which, at the temperatues reached during heating andsintering, do not deleteriously affect the dielectric properties of thedielectric composition used by reacting therewith. Those skilled in theart are familiar with the effects of various materials and can readilymake proper choices thereof. It should be mentioned here that, e.g. bychoice of one or more of the several means discussed above, theopen-structured areas of ceramic chips can be varied not only in toto,but that different areas and portions of areas may be more or lessporous than others. This enables the production of chips in which theportions of the porous strata adjacent the exposed end faces thereof areless porous or have finer pores than the portions lying nearer thecenter of the chips.

Further, it will be understood that there are available commerciallymany media or vehicles which can be used for forming films and/or makingscreen printing compositions from fine particles according to thepresent invention and that many more such vehicles are known to thoseskilled in the art. Essentially, the purpose of such a medium or vehicleis to suspend the particles and provide a temporary or fugitive bondtherefor during formation of leaves and/or layers and the consolidationof a plurality thereof into green bodies prior to sintering. In thesintered bodies the temporary or fugitive bond, as well as anycombustible particulate material used, has disappeared. Accordingly, themedium or vehicle used is a matter of choice or convenience and in mostinstances any change in the composition bonded thereby will require somechange or modification, e.g. adjustment of viscosity, in any medium orvehicle employed.

Firing of small ceramic units or chips to sinter them into unitarybodies is preferably carried out in a kiln. An electrically heatedtunnel kiln or furnace is preferred but other kilns or other heatingmeans may be employed. Ordinarily an oxidizing atmosphere is used but,when convenient, other atmospheres can be employed. The temperature,atmosphere, and the time of firing will depend on the ceramiccompositions employed. Those skilled in the art are familiar with suchdetails, as pointed out above, and with the fact that in general thesintering time necessary varies inversely with the temperature and viceversa. As indicated above a prolonged period of heating at relativelylow temperatues is preferred for removal of the temporary bonds used inthe leaves and printed areas and any burn-out particles employed. If toorapid heating is employed, expansion of gases formed in thedecomposition or burning of these materials may rupture the chips.

In FIG. 6 there is illustrated a typical ceramic multilayer circuitstructure 50 such as is used for hybrid integrated circuits. Thestructure 50 has a ceramic matrix 52 and a plurality of conductors 54extending into and through the matrix. The thickness of both conductorsand matrix is exaggerated in FIG. 6 for convenience in viewing.Hitherto, such structures have been expensive to produce and normallywould be made by screen printing a metallic paste containing a noblemetal such as palladium or platinum in the desired conductor patterns onsheets of desired thickness of a temporary bonded, electricallyinsulating, ceramic material such as alumina powder, consolidating theseveral sheets, and sintering the alumina sheets into a unitary body.

As mentioned above, such ceramic multilayer circuit structures may alsobe produced by techniques essentially similar to the processes disclosedabove for producing monolithic capacitors. The necessity for usingexpensive noble metals as conductors is thus avoided since firing ofmetal and sintering the ceramic concurrently is not necessary. Onemethod for producing such a structure as that shown in FIG. 6 by thetechnique of the present invention will be briefly described withreference to FIG. 7.

The sheets or films A, B, and C shown in FIG. 7 are formed in thedesired size, shape, and thickness by casting, molding, or the like, adesired electrical insulating, ceramic composition, for example, finelydivided alumina, using a resin, ethyl cellulose, or the like as atemporary bond therefor. Pseudoconductors following the paths of thedesired conductors in and/or on the structure as shown at 60 are thenscreen printed on the sheets or films using, for example, a ceramicmaterial in a suitable vehicle or squeegee medium, the ceramic materialbeing one, e.g. coarser alumina powder, which upon firing to sinteringtemperature will develop an open structure. The sheets are assembled,consolidated, and heated to sinter them into a unitary body, all in thesame manner as described above in connection with the production ofmonolithic capacitors. As with the latter, the unitary or monolithicbody produced by heating comprises a dense matrix of the ceramicinsulating composition having therein open-structured areas of ceramicmaterial, which may be the same or different in composition, asubstantial portion of the volume of such areas comprisinginterconnected voids. Each of said areas extends to at least one regionon an outer face, e.g. an edge face, of said body.

Conductors in and through said bodies may be formed by introducing intothe open-structured areas a suitable conductive metal in accordance withone of the procedures described below. After such impregnation, leadsmay be attached, by suitable known means, to exposed conductors wheredesired and small components such as transistors, diodes, etc., may besoldered at predetermined points, leads therefrom extending if desired,to underlying conductors 54 through holes 62 provided originally in oneor more of the ceramic sheets. If desired, one or more of the holes 62may be filled with the material employed to form the pseudoconductorswhen such material is applied to the faces of the sheets.

Although other procedures may be employed, a convenient and efficientway to provide conductive metal in the open-structured areas of small,sintered, ceramic bodies or chips or ceramic, multilayer, circuitstructures produced as described above is to inject the metal therein.Typical infiltration or injection procedures are set forth in thefollowing examples.

EXAMPLE 6

A plurality of sintered chips made in accordance with Example 1 areplaced in a bath of a molten metal alloy consisting of 50% Bi, 25% Pb,12.5% Sn and 12.5% Cd. The molten metal is held at a temperature fromabout 100° C. to about 125° C. in a suitable closed vessel. Afterintroduction of the chips, the pressure in the vessel is reduced toevacuate the open-structured strata of the chips and the pressure isthen raised to about 14 kg/cm² to force the molten metal into theinterconnecting pores of such strata. The chips after removal from thebath contain electrodes formed by deposit of the alloy in theopen-structured strata between the dense dielectric strata and, afterthe provision of termination electrodes in any desired manner, aresatisfactory monolithic capacitors.

It will be understood that other molten metals can be used forimpregnation of the open-structured areas or strata of ceramic chips ofthe types described above or of multilayer circuit structures as abovedescribed. For example, there may conveniently be used instead of thealloy specified in Example 6) the metals lead, aluminum, copper, zinc,tin and cadmium and alloys containing one or more of these metals. Othermetals are also usable but because of their higher cost, higherresistivity, greater ease of oxidation and/or high melting points, theyare not as desirable for forming electrodes. Examples of the many otheralloys that can be conveniently used are: Pb 25%, Sn 10%, Bi 63%, In 2%;Al 4%, Cu 1%, balance Zn; Cu 28%, Ag 72%, and various brasses andbronzes. As with the relatively pure metals, however, the cost,resistivity, ease of oxidation, and melting point of an alloy affectgreatly its desirability for carrying out the present invention.

In general, it has been found desirable to employ as internal electrodesor conductors, metals which do not easily wet the ceramic chips and/orcircuit boards into which they are injected. By avoiding combinations inwhich the ceramic is readily wet by the metal, it is possible to preventor minimize undesirable surface deposits of the metal which wouldrequire removal to preclude possible shorting.

In the conventional manufacture of monolithic capacitors, there is noproblem in providing a termination electrode on each end of thecapacitor units to electrically connect the exposed internal metalelectrodes thereon since the metal electroding pastes commonly employedfor this purpose do not require heating to a temperature higher than themelting point of the internal electrodes. The same is true of monolithiccapacitors produced by deposition of metal in open-structured strata offired ceramic chips by any of the procedures described in the saidcopending application when the melting point of the metal so depositedis higher than the temperature required to supply the terminationelectrodes. When, however, as may occur in carrying out the presentprocess, the metal deposited in the open-structured areas or strata ofceramic chips or circuit boards is liquid at a temperature equal to orlower than the temperature employed in applying the terminationelectrodes, the provision of the latter may present problems.

In the manufacture of monolithic capacitors by the process of thepresent invention, it has been found useful in many cases to providepenetrable barriers at the ends of the ceramic chips before injectingmolten metal into the open-structured strata of the chips. Such barriersshould be easily provided, should be of material having a melting pointhigher than the temperature at which the metal internal electrodes areinjected, and should be resistant to attack or dissolution in the bathof molten metal used for the internal electrodes. They allow evacuationof air from the open-structured areas of strata of fired ceramic chipssuch as those produced in accordance with any of Examples 1-5 and theinjection therein of molten metal to form interior electrodes. They alsoserve to restrict flow from such areas or strata when the pressure inthe vessel is released. Similar results are obtained by the use of suchbarriers on the desired faces of multilayer circuit structures accordingto the invention.

Suitable penetrable barriers can be formed in several ways. For example,when low-melting metals are used for infiltration of the unitary ceramicbodies, a coating of a commercial palladium-silver or palladium-goldelectroding paste can be applied to the surfaces of sintered chips atwhich porous strata are exposed and fired in the conventional manner.The coherent end electrode thus formed is penetrable to the moltenmetal.

When higher temperatures are required for infiltration of metal into theporous areas or strata of ceramic bodies, it has been found feasible toapply over such areas or strata on faces of the bodies a coating of aceramic material which is fired to form a penetrable, porous, ceramicbarrier. The ceramic material may be applied to the green ceramic chipsand fired at the same time as the latter or may be applied to thealready sintered chips and then fired.

The use of an end or termination electrode as a penetrable barrier isdescribed in the following example:

EXAMPLE 7

Porous end termination electrodes are applied to a plurality of sinteredceramic chips substantially like those produced in accordance withExample 1 by coating the end faces (i.e. the faces on which the porousstrata are exposed) of the chips with a commercial palladium-silverelectroding paste (DuPont No. 8198) and firing the thus-coated chips atabout 880° C. the firing cycle being about 1 hour.

Using apparatus similar to that used in Example 6, the chips are placedin a heated pressure vessel above a bath of molten tin held at about315° C. The vessel is closed and through a suitable connection theinterior of the vessel is evacuated to a pressure of about 60 mm ofmercury to remove air from the porous strata of the chips. The chips,which have now been sufficiently heated so that no substantial thermalshock will result, are then lowered into the tin bath and the pressurein the vessel is raised, by supplying a compressed gas, such asnitrogen, thereto, to about 17.5 kg/cm². The chips are then removed fromthe melt and, after cooling in the vessel to below the melting point oftin, the gas pressure in the vessel is released and the chips arewithdrawn from the vessel, adhering tin being removed if necessary.Microscopic inspection of broken chips reveals that tin has been forcedinto the porous strata thereof and the impregnated chips are verysatisfactory monolithic capacitors.

As indicated above, the penetrable barriers employed in injecting orimpregnating open-structured areas need not be electrically conductive,termination electrodes. The following three examples illustrate this.

EXAMPLE 8

Unfired ceramic blocks or chips such as ones prepared in accordance withExample 4 are employed. The end faces of a plurality of the chips, i.e.the surfaces at which the alternate layers of screened-on compositionare exposed, are coated, conveniently by painting, with the same screenprinting composition as is applied to the leaves of the resin-bonded,dielectric, ceramic composition. The coated chips are then subjected toheating in air to eliminate the combustible materials and fired in airat about 1325° C. to sinter the ceramic. The resulting fired ceramicchips have alternate dielectric strata and open-structured strata andend barriers which are permeable to molten metal.

The fired chips are impregnated with molten tin in the manner describedin Example 7. After removal of the metal-impregnated chips from thepressure vessel and cooling, the ceramic barriers and any undesiredmetal adhering to the surfaces of the chips are removed, for example, bysandblasting, and electrically conducting termination electrodes areapplied in accordance with any desired procedure. The resultantmonolithic capacitors are very satisfactory.

EXAMPLE 9

Unfired ceramic blocks or chips such as ones produced in accordance withExample 5 are used. In procedure similar to that in Example 8, the endfaces of a plurality of the chips are coated, by painting or dipping,with the liquid composition used in Example 5 for casting the sheetsemployed in forming the porous strata in the chips. The coated chips arethen heated in air to burn out the combustible materials and sintered inthe manner described in Example 5 to obtain small ceramic bodies withporous strata that can be injected with metal through the porous,open-structured, ceramic barriers formed during sintering.

The fired chips are impregnated with a molten metal alloy consisting of72% Ag and 28% Cu using essentially the procedure described in Example7. The temperature of the alloy during impregnation is preferably about880° C. When the chips are impregnated and cooled, and aftersandblasting to remove the ceramic barriers if this is necessary toobtain good electrical contact with the internal electrodes, conductiveend terminations are applied to form monolithic capacitors.

In the two immediately preceding examples, the ceramic barriers areapplied to the end surfaces of the ceramic chips before the latter aresintered and are thus sintered at the same time. In the followingexample a penetrable ceramic barrier is applied to the chips subsequentto sintering them.

EXAMPLE 10

A readily spreadable paste is prepared by blending finely dividedborosilicate glass having a melting point of about 1080° C. in about 1:2weight ratio with a liquid vehicle formed from 80 ml pine oil, 14 gacrylic resin, 1.5 g lecithin dispersing agent and sufficient, about 1to 2 g ethyl cellulose to impart the desired viscosity. This paste isapplied by spreading it on the end faces (where the porous strata areexposed) of sintered ceramic chips such as are produced by Example 5.The coated chips are then heated to about 790° C. to burn off thevehicle of the applied paste and provide a porous, sintered glassbarrier on the chip end faces.

The thus-prepared chips are impregnated with molten lead by the sameprocedure employed in the metal impregnation of chips described inExample 7 the temperature of the lead bath during impregnation beingabout 450° C. After sandblasting or otherwise removing the glassbarriers and any undesired surface metal deposits the chips may beformed into satisfactory monolithic capacitors by providing endtermination electrodes by any known or desired procedure.

Extensive experiments have shown that by the process of the presentinvention monolithic capacitors with internal electrodes of infiltratedbase metal can be produced with capacitances substantially the same asthose of monolithic capacitors of the same size and number of layersproduced by conventional processes with noble metal internal electrodes.This has been demonstrated with dielectric compositions havingrelatively high dielectric constants as well as ones with relatively lowdielectric constants.

The structure obtained when a permeable barrier is provided on an endface of a ceramic chip preparatory to forming a monolithic capacitor isillustrated in FIG. 8 of the accompanying drawings. In this figure,which is a fragmentary, enlarged sectional view, the strata 70 representsintered ceramic dielectric material, the numeral 71 designates theopen-structured strata, alternating with the first-mentioned strata,into which molten metal is injected to form internal electrodes, and thenumeral 72 designates the open-structured, penetrable barrier throughwhich the molten metal is injected. The showing in FIG. 8 is somewhatdiagrammatic since when a ceramic penetrable barrier is used, it is sosintered to the ceramic chip as to unitary and frequently there is noclear line of demarcation between the barrier and the chip.

As will be clear to those skilled in the art, the permeability of thepenetrable barriers employed may be adjusted as desired. This can bedone, for example, by the inclusion of greater or lesser amounts ofburn-out material, such as carbon black, in the compositions used forproviding such barriers and/or by adjustment of the particle size of thesolid materials in such compositions. Other procedures for suchadjustment may be used if desired. It will be understood that in someinstances termination electrodes may be applied to bodies, by anydesired method, over penetrable ceramic barriers subsequent to theinjection of metal therethrough into open-structured areas of the body.However, to ensure good electrical contact of such electrodes with theinfiltrated internal electrodes, it is frequently desirable to removethe barriers before applying termination electrodes. This can be, aspointed out above, readily accomplished by sand blasting.

Although Examples 6-10 are directed to the production of monolithiccapacitors by the injection of metal into the open-structured strata ofsintered ceramic chips, it is evident that similar techniques, includingthe use of penetrable barriers, if desired, may be used in providingconductors in multilayer circuit structures such as are describedherein.

It will also be evident that certain other sintered ceramic chips ormatrix structures can have metal injected into them through, if desired,penetrable barriers. Such matrix structures include structures such asare described in U.S. patent application Ser. No. 400,242, filed Sept.24, 1973, wherein substantially void, planar areas intervene betweenadjacent dielectric or insulating strata, and such as are described inU.S. patent application Ser. No. 400,243, filed Sept. 24, 1973, whereinthe adjacent dielectric or insulating strata in the matrix have at leastone distinct inorganic pillar between them and wherein, when there are aplurality of pillars, substantially all of said pillars are distinct andseparated. Although such void planar areas and pillars are not, bystrict definition, strata, they are of such an open-structured characterthat when the terms "open-structure" and "open-structured" are employedin the claims the terms should be interpreted as including suchstructures.

The production of such matrix structures and the production ofcapacitors and multilayer circuit structures from such matrices isclearly and fully described in the patent applications referred to,which are hereby incorporated herein by reference. However, to give ageneral idea of the disclosures in said former applications certaindrawing figures from said application have been incorporated in thepresent application and described.

FIG. 9 shows a greatly enlarged, fragmentary, sectional view through asintered ceramic matrix, such as is used in forming a monolithiccapacitor, obtained in accordance with the teaching of application Ser.No. 400,242. In this view the sintered, ceramic, dielectric strata 75have substantially void, planar areas 77 intervening therebetween andavailable for injection thereinto of molten metal to form internalelectrodes. The void areas 77 can be formed by heating a compositecontaining alternating strata of temporarily bonded, finely divided,ceramic dielectric material and pseudo-conductive layers of a materialthat will volatilize or burn out when the composite is heated to removethe latter and to sinter the dielectric material.

FIGS. 10-13 are substantially copied from application Ser. No. 400,243.FIG. 10 shows a greatly enlarged, fragmentary, sectional view through asintered ceramic matrix such as is used in forming a monolithiccapacitor. In this figure, the ceramic dielectric strata 78 areseparated by relatively void spaces 79 which contain pillars 81. FIG. 11is a very greatly enlarged view of a bonded ceramic aggregate. Suchaggregates have been used satisfactorily as pillars.

As shown in FIG. 11, before firing the fine ceramic particles 82 arebonded with a thermally-fugitive bond 83. Such aggregates can be readilymade, for example, by forming a mixture of finely divided ceramicdielectric material of the kind used for the dielectric leaves and atemporary bond such as employed therefor and allowing the mixture todry. The mass is then broken up and bonded aggregates of the desiredsize are obtained by selective sieving. The aggregates may be firedunder proper conditions to sinter together the individual ceramicparticles therein. However, it will be seen that by using for granules,unfired aggregates such as described, sintering of the ceramic particlesin the aggregates will take place contemporaneously with the sinteringof the dielectric layers, and no problems are likely to arise from theunequal shrinkage that may occur when different materials are employed.Whether the aggregates used are fired or unfired, there is, of course,no danger of deleterious reaction between the granules and thedielectric material. While it should not be soluble in the solventemployed in depositing the pseudo-conductive layers, the nature of thetemporary, thermally fugitive bond used in forming such aggregates isnot particularly critical, a number of suitable materials being usable,e.g. those usable in forming the dielectric ceramic sheets.

Another possible procedure for obtaining pillars in a ceramic matrix isto deposit, e.g. by screen printing, a layer consisting of heat-fugitivematerial on each of a plurality of sheets of finely divided ceramicmaterial bonded with a heat-fugitive bond, but leaving in said layer oneor more spaced-apart areas that form holes through said layer. When aplurality of sheets having such layers are consolidated and fired toremove the thermally-fugitive materials and to sinter the ceramicmaterial, the sheets above and/or below the open areas or holes willdeform sufficiently to produce ceramic pillars in said holes. Aftercompletion of the firing, of course, such pillars stand in the cavityresulting from the disappearance of the thermally-fugitive materialconstituting the layer.

FIGS. 12 and 13 illustrate diagrammatically the last-mentionedprocedure. FIG. 12 is a fragmentary plan view, greatly enlarged, whichshows two sheets 84 of finely divided ceramic material bonded with asuitable thermally-fugitive bond, between which has been provided alayer 86 consisting of thermally-fugitive material. A plurality ofspaced holes 85 have been left in the layer 86. FIG. 13 is a furtherenlarged, fragmentary sectional view, taken along the line 13--13 ofFIG. 12. It shows a portion of the body illustrated in FIG. 12 after thebody has been consolidated and fired in suitable manner to remove thethermally-fugitive materials and to sinter the ceramic material. Thenumeral 97 designates a ceramic pillar in the planar space 99 thatresults from removal of the thermally-fugitive layer 86. Such pillar hasbeen formed by deformation of the ceramic sheets 91 above and below andextrusion of ceramic material therefrom into the hole 95. It will beunderstood that, although FIGS. 12 and 13 illustrated only two sheets ofceramic and an intervening layer of thermally-fugitive material, informing a monolithic capacitor many such sheets would be superposed withsuch intervening layers and that similar pillars would be formed inothers of the holes 95 during the consolidation and firing of the stackof sheets and layers. The shape of the holes 95 is not critical and anyconvenient shape can be used. Because of the difficulty encountered inproviding very small holes in the layers of thermally-fugitive material,the smallest horizontal dimensions of such holes will ordinarily beseveral times the thickness of the thermally-fugitive layer in whichthey are formed. In any case, however, the smallest horizontal dimensionshould be at least as great as the thickness of such layer. The numberand arrangement of the holes may vary in accordance with the number andplacement of the pillars desired. Pillars of the type here described canbe used in forming capacitors and also, in some cases, in formingmultilayer circuit structure matrices where the size of the channels forthe conductors permits.

It should be understood that the function of the pillars is to providesome support in the cavities or channels of fired bodies according tothe invention, whereby the compressive strength of the bodies will beincreased sufficiently to reduce possibility of breakage in handling.Obviously the number of pillars necessary to give the desired strengthwill vary with the size and shape of the cavities or channels. Tomaintain an open structure in the cavities or channels the pillarsshould not exceed in volume 40% of the volume of the cavity or channeland in most cases 10% by volume or even less will be desirable. Indeed,where the cavity or channel is very small only a single pillar may bedesired. When the pillars are formed by ceramic or metallic granules ina pseudo-conductive layer they will, of course be randomly located.However, as mentioned above, they should be separated so as to provideno substantial impediment to entry of conductive material into thecavities and therefore the concentration of granules in thepseudo-conductor should be no greater than required to obtain thedesired strength. Preferably the pillars are of a diameter approximatingthe thickness of the pseudo-conductor in which they are held.

The pressure required for the impregnation of open-structured areas ofceramic chips or ceramic multilayer circuit structures with molten metalaccording to the invention will vary with the type, configuration, anddimensions of such areas. Also affecting the required pressure are theviscosity of the molten metal and the surface energy thereof relative tothat of the contents, if any, of the open-structure areas. In somecases, it may be necessary to make preliminary experiments to discoverthe optimum pressure to use. However, it has been found that in the useof metals of medium and low melting points, pressures greater than about17.5 kg/cm² are not necessary. It should be understood that the pore orvoid size in a penetrable barrier may, if desired, be less than that inthe open-structured areas of the body on which the barrier is applied.

End or termination electrodes can be formed not only with metallicelectroding pastes of conventional types, but also, when suitable, byapplying to faces of bodies coatings of air-drying conductive metalpaints, electroless nickel, indium-gallium alloy, and sprayed metal. Itmay be noted that flameor arc-sprayed metal is usually deposited in arather porous layer. Hence, such deposits can be used, if desired, asconductive penetrable barriers.

It will be understood that where bodies having open-structured areashaving a structure such as shown in FIG. 9 or FIG. 10 are covered withan end termination, the resultant bodies will resemble the structureillustrated in FIG. 8 except that the open-structured areas will be asshown in FIG. 9 or FIG. 10.

Monolithic capacitors according to the present invention may vary widelyin size. Not only may the dimensions of the capacitor be varied, but thenumber and thickness of the strata therein may also vary. Although inmost cases it is preferred to make the dielectric strata thicker thanthe conductive layers, this is subject to variation as desired.Capacitors as small as 2.0 mm× 3.0 mm×0.9 mm with 20 dielectric strataas thin as about 0.03 mm and 19 porous strata as thin as about 0.015 mmcan be readily made, and larger ones are, of course, possible.Capacitors of any desired capacitance may be obtained according to theinvention by proper choice of dielectric material and the size,thickness, and number of the strata and conductive layers. It will beunderstood that one or more extra or additional dielectric leaves orsheets may be placed at the bottom and/or top of a stack of alternateddielectric leaves or sheets and leaves or sheets containing acomposition adapted to form open-structured areas. This is often done togive additional mechanical strength to the capacitors and/or to adjusttheir thickness. An unprinted leaf or leaves of a dielectric ceramiccomposition can be used. However, the presence of a painted ceramic filmon the top dielectric film or leaf of such a stack will ordinarily notbe detrimental since after sintering the resultant exposed porousdeposit will either not hold an electrode material or such material canbe easily removed, for example by sanding.

In the foregoing description and the examples, the leaves of dielectricand/or pseudo-conductive material and the capacitors formed therefromare rectangular. However, the present invention comprehends capacitorsof other shapes. Thus, if desired, monolithic capacitors according tothe invention may be triangularly shaped. In such case, obviously,pseudo-electrodes, alternate open-structured areas, and the electrodesformed therein can not be exposed on opposite edge faces. Consequently,it will be understood that in the appended claims the term "edge region"is used comprehensively to indicate an area on an edge face of a bodyregardles of the geometry of the body and whether it has one or aplurality of edges.

As used herein, a "thermally-fugitive" or "heat-fugitive" material isone which, under the conditions of one of the processes hereindescribed, volatilizes as such or is wholely converted, with or withoutoxidation, into products that volatilize. Also, as used herein the term"dense" means that the material absorbs substantially no water whenimmersed therein.

The terms of position or direction, such as upper, lower, left, right,etc., used herein are with reference to the accompanying drawings andshould not be interpreted as limiting the invention or requiring anyspecific positioning of the capacitors in use.

Except as otherwise indicated, ratios, percentages, and parts referredto herein are ratios, percentages, and parts by weight.

It will be evident from the foregoing description that many variationsand modifications of the present invention are possible withoutdeparting from the spirit thereof. For example, instead of using leavesof temporarily bonded, powdered dielectric or insulating ceramicmaterial which are formed as distinct entities, sheet-like films of suchmaterial in a suitable medium or vehicle may be formed by screenprinting on underlying sheets or layers. Also, for example, instead ofscreen printing the compositions which develop an open structure onfiring, such compositions can be painted on or applied in other ways.Further, although a self-sustaining body is desired for firing, thestack of leaves or of leaves and the layers thereon need not be pressedto consolidate the stack. In some cases, for example, rolling of thestack as it is built up, will provide sufficient consolidation. Also, ifdesired, the open-structured areas or strata can be partially filledwith metal by one of the procedures described in the abovementioned U.S.Pat. No. 3,679,950 and additional metal may be injected into thepartially filled areas or strata by the process of the presentinvention. In such case, the metal injected or infiltrated may be thesame as that first introduced or a different metal can be used.

I claim:
 1. A sintered, unitary ceramic body comprising: a plurality ofstrata of a dense dielectric or insulating ceramic composition, saidstrata alternating with open-structured areas substantially parallelwith said strata and extending to edges of said body, each of saidopen-structured areas containing at least some solid material andalternate ones of said open-structured areas extending to different edgeregions of said body; and a penetrable barrier over each of said edgeregions, said barriers permitting molten metal to be forced by pressureinto said areas.
 2. A body as set forth in claim 1 in which said areasare in the form of strata of ceramic material having a network ofinterconnected pores.
 3. A body as set forth in claim 1 in which saidpenetrable barriers are end termination electrodes.
 4. A body as setforth in claim 1 in which said penetrable barriers are end terminationelectrodes. pg,34
 5. A sintered, unitary ceramic body comprising: aplurality of strata of a dense dielectric or insulating ceramiccomposition, said strata alternating with open-structured areassubstantially parallel with said strata and extending to edges of saidbody, alternate ones of said open-structured areas extending todifferent edge regions of said body; and a penetrable ceramic barrierover each of said edge regions, said barriers permitting molten metal tobe forced by pressure into said areas.
 6. A body as set forth in claim 5in which said areas are in the form of strata of ceramic material havinga network of interconnected pores.
 7. A body as set forth in claim 5 inwhich said areas are substantially void and planar.
 8. A body as setforth in claim 5 in which adjacent ones of said strata have at least onedistinct inorganic pillar between them and wherein, when there are aplurality of pillars, substantially all of said pillars are distinct andseparated.